1. Field of the Invention
The field of this invention relates to copolyimides prepared from tetramethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride (TMCDA) and a mixture of diamines. These novel copolyimides are useful in preparing molded articles, fibers, films, laminates and coatings.
2. Background
It is known to make copolyimides from pyromellitic dianhydride and aromatic diamines. This is disclosed in U.S. Pat. No. 3,179,634 (1965). British Patent Specification No. 570,858 discloses various processes for making fiber forming polymers. The Japanese Patents listed below disclose the preparation of polyimides starting with cyclobutane-1,2,3,4-tetracarboxylic dianhydride.
JA 7123917-S27, JA 7137733-S44, JA 7137734-S44JA 7219710-T23, and JA 72199098-T23. The article by F. Nakanishi and M. Hasegawa, Polymers, 14, 440 (1973) discloses the use of cyclobutane-1,2,3,4-tetracarboxylic dianhydride and 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride in the preparation of polyimides: In reviewing all these references, it is clear that the use of TMCDA to form copolyimides useful as moldings, films, fibers, laminates, and coatings has not been contemplated in the prior art. Copending applications U.S. Ser. Nos. 286,696, 286,697, and 294,345 all filed 724-81 disclose homopolyimides of TMCDA and a diamine and copolyimides of TMCDA and a second dianhydride with a diamine and glass reinforced polyimides and copolyimides. All these companion applictions are incorporated herein by reference.
The general object of this invention is to provide novel copolyimides based on TMCDA and a mixture of diamine moieties. A more specific object of this invention is to provide copolyimides from TMCDA moieties and mixtures of aliphatic, cycloaliphatic, araliphatic and aromatic moieties. Another object is to provide a process for the manufacture of copolyimides, from TMCDA and a mixture of diamines.
We have found that novel copolyimides can be formed by reacting TMCDA with a mixture of diamines. TMCDA reacts readily with the diamine mixture to form a high molecular weight copolyimide. In the novel process both aliphatic and aromatic diamines can be copolymerized with TMCDA in the melt to form high molecular weight copolyimides.
Our process for the manufacture of the novel polyimides comprises reacting about equal molar amounts of TMCDA with or a mixture of primary diamines. The molecular ratio of TMCDA to the mixture of primary diamines may be in the range of 1.3:1.0 to 1.0:1.3 preferably in the range of 1.00 to 1.00. In a suitable method, the reaction is conducted as a batch reaction at a temperature of about 130.degree. to 300.degree. C. for a period of about 0.25 to 6.0 hours in a nitrogen containing organic polar solvent such as 1-methyl-2 pyrrolidinone (NMP), N,N-dimethylacetamide or pyridine. The polycondensation can also be carried out as a continuous process. The polycondensation can suitably be carried out at a temperature of 0.degree. C. to 200.degree. C., preferably at a temperature of 50.degree. to 100.degree. C.
The novel copolyimides of this invention have the following recurring structure: ##STR1## wherein R is a divalent aliphatic or aromatic hydrocarbon radical. The radicals R and R' are different and may be divalent aliphatic hydrocarbons of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising --O--, methylene, ##STR2## --SO--, --SO.sub.2 --, and --S--radicals. The radicals R and R' are derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, dodecamethylene diamine, 4,4'-diaminodicyclohexylethane, xylylene diamine and bis(aminomethyl)cyclohexane. Suitable aromatic diamines useful in our process include para- and meta-phenylenediamine, 4,4'-oxydianiline, thiobis (aniline), sulfonylbus (aniline), diaminobenzophenone, methyleneis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis (2-methylaniline), thiobis (2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890(1970) and U.S. Pat. No. 4,016,140 (1972) both incorporated herein by reference. The preferred diamine mixtures are 1,6-hexamethylenediamine and 1,12-dodecanediamine, 1,6-hexamethylenediamine and 4,4'-oxydianiline, 1,12-dodecanediamine and 4,4'-oxydianiline and 1,6-hexamethylenediamine and ethylene diamine. The ratio of the two diamines may be in the range of 19:1 to 1:19 preferably 3:1 to 1:3.
In some cases the copolyimide may be further polymerized under "solid state polymerization" conditions. The term solid state polymerization refers to chain extensions of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. The solid state polymerization can be carried out below the melting point of the copolyimide and can be conducted in several ways. However all techniques require heating the ground or pelletized polyimide below the melting point of the polyimide, generally at a temperature of about 200.degree. to 300.degree. C. while either sparging with an inert gas such as nitrogen or operating under vacuum. In cases where the copolyimides have a low melt temperature, they can be polymerized in the melt under vacuum in thin sections or using thin film reactors known in the art.
Injection molding of the novel copolyimide is accompanied by injecting the polyimide into a mold maintained at a temperature of about 23.degree. to 200.degree. C. In this process a 20 second to 1 minute cycle is used with a barrel temperature of about 200.degree. C. to 350.degree. C. The latter will vary depending on the T.sub.g and T.sub.m of the polymer being molded.
The novel polyimides have excellent mechanical and thermal properties and can readily be molded into useful articles or formed into fibers, films, laminates or coatings. Infrared spectra of the polyimides has confirmed the copolyimide structure and also shows the absence of any amide structure in the copolyimides. Carbonyl band heights are also consistent with the groups in the polyimide structure.
Analysis of the TMCDA-diamine copolyimide by thermal gravimetric analysis shows excellent stability. This is demonstrated by the fact that under nitrogen atmosphere the 1 percent weight loss occurs at a temperature of 310.degree. C. and main weight loss occurs at a temperature of about 390.degree. C. Glass transition temperature T.sub.g of the polyimide varied with the particular diamine used as shown in the Examples.
Diamines with the amino groups attached directly to the aromatic ring are suitably copolymerized with TMCDA by solution condensation in organic polar solvents. Useful polar solvents include N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, N,N-dimethylformamide, dimethylsulfoxide and the like.
The copolyimide was cast into films. The films were heated at a temperature of 200.degree. C. for 10 minutes. The dry film was 10 mm in thickness and was transparent.
We have found that the copolyimides of this invention are improved by the addition of refinforcing material particularly the mechanical properties of the polyimides are improved if these copolyimides contain from about 25 to 60 percent by weight glass fibers, glass beads, industrial minerals such as talc or graphite or mixtures thereof. In the preferred range the polyimides contain 30 to 40 percent by weight of the glass fibers, glass beads, industrial minerals or graphite or mixtures thereof. Suitably reinforcing materials can be glass fibers, glass beads, glass spheres, glass fabrics. The glass fibers are made of alkali-free boron-silicate glass or alkali containing C-glass. The thickness of the fiber is suitably on the average between 3 and 30 mm. It is possible to use both long fiber with average lengths of from 5 to 50 mm and also short fibers with an average filament length from 0.05 to 5 mm. In principle, any standard commercial-grade fibers especially glass fibers may be used. Glass beads ranging from 5 to 50 mm in diameter may also be used as a reinforcing material.
The reinforced copolyimide polymers may be prepared in various ways. For example, so-called rovings endless glass fiber strands are coated with the polyamic acid melt and subsequently granulated. The cut fibers or the glass beads may also be mixed with granulated polyamic acid and the resulting mixture melted in a conventional extruder, or alternatively the fibers may be directly, introduced into the polyamic acid melt through a suitable inlet in the extruder. Injection molding of the novel glass-filled polyimide is accomplished by injecting the polyimide into a mold maintained at a temperature of about 23.degree. to 200.degree. C. In this process a 25 to 28 second cycle is used with a barrel temperature of about 200.degree. to 350.degree. C. The injection molding conditions are given in Table 1.
TABLE I ______________________________________ Mold Temperature 23 to 200.degree. C. Injection Pressure 15,000 to 19,000 psi and held for 1 to 3 seconds Back Pressure 100 to 220 psi Cycle Time 25 to 28 seconds Extruder: Nozzle Temperature 200 to 350.degree. C. Barrels: Front heated to 200 to 350.degree. C. Screw: 20 to 25 revo- lutions/minute ______________________________________